The present invention relates to a melt spinning process stably practicable for a long period of time.
More specifically, the invention relates to a process for melt spinning aromatic polyesters to produce aromatic polyester fibers having high strength and high modulus of elasticity, which process is stably practicable for a long period of time.
Recently, aromatic polyesters showing anisotropy in the molten state have been found to give polyester fibers having high strength and high modulus of elasticity. And the melt spinning process has many advantages in that no solvent is used and existing apparatus can be employed. However, the aromatic polyesters capable of giving polyester fibers having high strength and high modulus of elasticity requires a high processing (spinning) temperature for the spinning, and therefore at the time of spinning, occurrence of increasing of viscosity and foaming due to the reactions such as decomposition, polymerization, crosslinking and the like cannot be avoided, and the viscosity of the melt extruded readily varies due to a remarkable temperature dependence. These make it difficult to continue the spinning stably for a long period of time.
While physical properties of the fiber can be improved, as known, by making the fiber fine (fine denier), it is difficult to spin the aromatic polyesters showing anisotropy in the molten state in a fine denier because of the cooling solidification rate thereof being extremely high. For example, minimizing of the hole diameter of the nozzle causes various problems such that a nozzle processing is made difficult and plugging of the nozzle readily occurs.
So far, different kinds of aromatic polyesters showing anisotropy in the molten state have been proposed, for example, in Published Examined Japanese Patent Application No. 482/1980, and the like. However, the embodiments disclosed therein are only on a laboratory scale and therefore not useful from industrial point of view. Thus, it has been desired to develop a melt spinning process industrially stably practicable for a long period of time.